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How do Analgesics work
Background Pain is a pleasant sensory and emotional experience associated with actual or potential tissue damage. In various body tissues, there are pain receptors (free nerve endings that transmit pain). These receptors respond to thermal, mechanical or chemical stimuli. When stimulated, these receptors generate an impulse which travels to the spinal chord and brain. When tissues become damaged, they release chemicals called prostaglandins and leukotrines that make the pain receptors more sensitive. These receptors then become more responsive to gentil stimuli, causing pain. Types of analgesics 1. Mild analgesics- Considered non-addictive, Used for mild pain relief including fever. Examples of mild analgesics includes Aspirin, Acetaminophen, Tylenol, Paracetamol, Phenacetin, Ibuprofen, and Non-steroidal anti-inflammatory drugs (NSAIDS). 2. Strong opiates- used for relief of severe pain. this includes Morphine, Heroin (Diacetylmorphine or Diamorphine) and Codeine. These are controlled substances that are addictive. 3. Local Anaesthetics- such as Lidocaine and Procain. 4. General anaesthetics- substances that act on the brain and produce reversible unconsciousness as well as in-sentivity to pain. There are many different types, but they can roughly be set into two classes: They are defined by the way in which they relieve pain. '''Opioids / '''narcotics (opiates and synthetic narcotics; all derived from opium) – act on brain receptors/inhibit the sensory neural pathways of pain *for short or long term pain relief *usually by prescription, prolonged use results in tolerance to it and physical dependence. Nonopoids / non-narcotics (inc: NSAIDS eg: aspirin) – act on the thalamus to inhibit synthesis prostaglandinsthereby raising the pain threshold. Prostaglandins are molecules involved in the peripheral perception of pain. - mostly for short term relief - without prescription - analgesic properties are not as strong as morphine and synthetic Opioids. - most commonly used of analgeiscs medication. - often combined with caffine or barbiturate sedative and sold for the relief of headache and backache etc. (A salt or ester of barbituric acid.) How Analgesics Work Mild Analgesics, such as Aspirin, work by indirectly blocking the enzyme-controlled synthesis of Prostaglandins. Prostaglandins constrict the blood vessels and thus, restrict blood flow and increase body temperature as less heat can escape from the tissue into the blood. They affect the hypothalamus (bodies heat regulating centre) which causes fever. These chemicals also increase the permeability of capillaries allowing water to pass out into nearby tissue causing swelling and pain. By restiricting the synthesis of Prostaglandins, mild analgesics can reduce pain, fever and inflammation. Chemical painkillers such as Endorphins and Enkephalins are produced naturally in the body. Enkephalins are naturally produced in the body as they are part of the brain and spinal cord that transmit pain impulses. These bind to neuro-receptors in the brain to produce relief form pain. The temporary loss of pain immediately after an injury is associated with the prodution of these chemicals. Strong analgesics (opiates) work by temporarily binding to the opiate receptors sites in the brain and prevents the transmission of the pain impulses without affecting the central nervous system. 'Thalamuse '''Fuction: motor control; receives auditory, somatosensory, and visual sensory signals; relays sensory signals to the cerebral cortex. '''Prostaglandins '''Discoverer thought they came from the prostate gland but we now know they exist and are synthesized in almost all cells of the body. They work where they’re made, and are like hormones in that they act as chemical massengers. '''Effects of Aspirin: ' Aspirin blocks an enzyme called cyclooxygenase, COX-1 and COX-2, which is involved with the ring closure and addition of oxygen to arachidonic acid converting to prostaglandins. The acetyl group on aspirin is hydrolyzed and then bonded to the alcohol group of serine as an ester. This has the effect of blocking the channel in the enzyme and arachidonic can not enter the active site of the enzyme. By inhibiting or blocking this enzyme, the synthesis of prostaglandins is blocked, which in turn relives some of the effects of pain and feber. Aspirin is also thought to inhibit the prostaglandin synthesis involved with unwanted blood clotting in coronary heart disease. At the same time an injury while taking aspirin may cause more extensive bleeding.